Electrical linear motors are used in various electromechanical actuators. Electrical linear motors are used as well to propel vehicles. For example, linear motors are used in magnetic levitation technology in which train passenger cars float above a concrete guide way and in other high speed “wheels-on-rails” trains. These types of linear motors are usually of the linear synchronous design with an active winding on one side of an air-gap and array of alternate pole magnets on the other side. These magnets can be permanent magnets or energized magnets.
Electrical rotary motors are used to propel vehicles and marine vessels such as boats and submarines. Electrical rotary motors for marine vessels utilize propellers to transform the rotary motor mechanical energy into working propulsion linear force. A disadvantage of utilizing propellers to propel a marine vessel is that the propeller creates a water rotational movement (swirl) in the water, thereby making the vessel more easily detected.
Using electrical linear motors for propelling a marine vessel, submarine, torpedo, or bathyscaphe, has several advantages over electrical rotary motors. For example, electrical linear motors can produce up to 3000 lbs. of linear driving force and therefore can provide increased velocities to the vessels. Also, the acceleration rate of electrical linear motors is up to 10 g. An electrical linear motor directly transforms its electrical energy into electrical linear motor propulsion force and therefore as a vessel's drive the electrical linear motor is simple, requiring few moving parts and not requiring mechanical transmissions such as propellers. As a result, ELM propulsion systems, consisting of electrical linear motors, whose rotors or stators simultaneously work as propulsions system thrusts, are more reliable than propulsion systems with rotary motors. The operation of electrical linear motors does not create pollution to the environment and is more energy efficient than electrical rotary motors. The ELM drive can be based on direct current (DC) or alternating current (AC).
In one known marine propulsion system employing a electrical linear motor as a drive (U.S. Pat. No. 7,604,520B2), the thruster subassembly and its two ball linear bearings are disposed inside of a guide tube. The permanent magnets are attached to the thruster subassembly by means of a magnet holder and placed outside of the guide tube in close proximity to electrical coil windings, which also are positioned outside and parallel to the guide tube. In such design embodiment the result of the interaction between magnetic field of magnets and electro-magnetic field of electrical coil windings is an axial force applied to the thruster subassembly permanent magnets. Then this force transforms into the axial resulting force, having a vector coinciding with the thruster subassembly longitudinal axis, and turning torque, which tries to turn thruster subassembly in the plane of the longitudinal section of the electrical linear motor propulsion system, thereby creating a radial load on two linear bearings supporting the propulsion system thruster subassembly. That radial load creates increased friction losses and heat emissions in linear bearings thereby resulting in linear bearings and thruster subassembly contact areas more intensive wear.
An advantage of the present invention is an electrical linear motor compact design that results in a single axial propelling force, vector of which coincides with the thruster subassembly longitudinal axis, thereby excluding a radial load on linear ball bearings and therefore providing more reliable and long-lasting operational life span for the electrical linear motor marine propulsion system.
Another advantage of new invention is that the increase of the resulting axial linear propelling force can be done by increase of the amount of electrical coil windings 3 (FIG. 1) placed in the electrical linear motor insert 2, and corresponding number of permanent magnets sets 4 installed on the magnet holder 12 without any change of insert outside diameter. For that purpose the geometry of the linear motor insert 2 (FIG. 1) internal space passage—place for thruster subassembly reciprocating movement—and also thruster subassembly permanent magnets holder 12 (FIG. 1) outside geometry have to be an equilateral triangular (case for 3 sets of electrical coil windings and magnets; FIG. 3), square (case for 4 sets of electrical coil windings and magnets; FIG. 4) pentagonal (case of 5 sets of electrical coil windings and magnets; FIG. 5). The amount of windings and magnets sets depends on how big the insert maximum outside diameter can be selected for each project.